Hormone profiles from Cook Inlet, Bristol Bay and aquarium beluga whales

Beluga whales (Delphinapterus leucas) from Cook Inlet (CI), Alaska, are listed as “endangered” because of dramatic declines in abundance, with no indications of population recovery. Serum samples from this population are exceedingly rare. Longitudinal samples from aquarium (AQ) belugas can potentially provide health assessment reference ranges for free-ranging beluga, including reproductive and metabolic hormones. We analysed serum hormone concentrations from CI (n = 6, three females and three males) and Bristol Bay (Alaska; BB; n = 5, four males and one female), alongside AQ (n = 3, two females and one male) belugas, to conduct physiological comparisons of reproductive hormones (progesterone, testosterone and total oestrogens) and metabolic hormones (total thyroxine, triiodothyronine and cortisol) in beluga serum. Oestrogen and progesterone profiles from January through May from two AQ female beluga were typical of non-pregnant, cycling females. CI and BB sex steroid concentrations were within AQ hormone ranges, with the exception of elevated progesterone concentrations in four potentially pregnant females. Both CI and BB belugas had elevated metabolic hormones, which may indicate greater metabolic effort required in the wild environment or capture response. Because sample collection from CI belugas is rare, analysis of even the few samples that we analysed may contribute to the conservation of the small and declining population of genetically distinct CI beluga whales. It is important that each sample collected from free-range CI belugas provides the maximum biological information possible. Continued comparison of hormones in AQ and free-ranging beluga will enhance the interpretation of health data in both groups.